This invention relates to electronic distance systems, and more particularly, to such systems of the non-contact, variable-inductance type.
Electromagnetic induction phenomena has been employed in prior measurement systems to sense proximity or distance changes between a transducer and a metal object. Such measurement systems are useful in a wide variety of applications particularly where it is impossible or undesirable that there be physical contact with the object defining a distance to be measured. Other applications include pressure transducers, accelerometers, electronic micrometers, dimension comparators, bore gages, limit gages, and liquid-metal level detectors.
Previous electromagnetic induction measuring systems have not achieved the degree of accuracy and stability necessary for concise and accurate distance measurements. Certain limitations have restricted the devolpment of these prior art systems, such as the difficulty in obtaining sufficient sensitivity and resolution over the effective measurement range of the system. This limitation results from the failure of the prior art systems to distinguish between the magnetic properties of the object and to compensate for these properties. Another limitation has been error caused by temperature variations. Temperature changes cause impedance changes in the object and in the inductive distance-measuring components of the system, and these impedance changes are reflected as a change in distance when in reality no such change may have occurred. A further problem with prior art systems has been that of non-linearity. Previously, it has been impossible to obtain a system that would register a linear output relative to the linear change in distance measured. Accordingly, it is a general object of this invention to overcome the aforementioned limitations of the prior art.
It is an object of this invention to provide an improved non-contact distance measurement system exhibiting high sensitivity and resolution over the effective measurement range of the system.
It is another object of this invention to provide an improved non-contact distance measurement system which is virtually insensitive to variations in temperature of the system or of the object whose distance is to be measured.
It is a further object of this invention to provide an improved non-contact distance measurement system having a high degree of linear relationship between the output provided and the distance measured.
Briefly to achieve these and other objects the present invention in one embodiment comprises a high frequency signal source, an inductive transducer and a reference impedance both connected in a signal phase network and to the source, and a means for comparing the signals from the transducer and the reference impedance to provide an output related to the distance between the transducer and the object. A circuit element such as a capacitor is connected in parrallel with the transducer for the purpose of enhancing the sensitivity and resolution of the system, for significantly reducing or effectively eliminating errors caused by temperature variations in the transducer or in the object measured, and for providing a high degree of linear relation between the output provided and the distance measured. Further, the system insures a high degree of linearity over the effective measurement range of the system.